1. Field of the Invention
The present invention relates to direct writing technology, more particularly, to an electron beam (EB) lithography system, a method for EB lithography, a program and a method for manufacturing a semiconductor device with direct writing.
2. Description of the Related Art
The mainstream of semiconductor device manufacturing has been a form of mass-producing single products, such as dynamic random access memory (DRAM). The costs of masks used for a photolithography process can be absorbed by mass-producing chips. Recently, however, the mainstream of production has changed from a large-volume small variety device, such as DRAM, to a large-variety small volume device, such as application specific integrated circuit (ASIC). Accordingly, conventional photolithography using masks has changed to direct writing by an EB lithography system.
In the direct writing using the EB lithography system, character projection (CP) lithography has been used to improve throughput. In the CP lithography, a plurality of character patterns are written collectively on a semiconductor wafer by using a perforated mask called a CP aperture, in which a repeatedly used graphic pattern is formed as a “character pattern”. According to CP lithography, the number of shots is reduced by batch-writing, thereby improving throughput.
However, in CP lithography, in the case of manufacturing of a large-variety small volume device, a character pattern is formed for each product at present. Accordingly, CP apertures must be frequently changed for each plurality of lots to be processed. Thus, a CP aperture change time and a beam adjusting time which is ancillary to the changing of the CP aperture are necessary, causing a reduction in capacity operating rate of the EB lithography system in some cases. Under the present circumstances a large throughput increase is difficult to achieve solely by hardware performance. Thus, there is a demand for production schedule in which a processing (writing) sequence of a plurality of lots is more productive.